JP2003303618A - Non-aqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery that is improved in battery capacity in substance in the voltage range in which the battery is actually used, while maintaining a high charge and discharge efficiency and good cycle characteristics. <P>SOLUTION: This is a lithium secondary battery that includes a negative electrode having a multi-layer structure comprising a first layer (21) made of mainly carbon and a second layer (22) made of mainly a material which has lithium ion conduction and is capable of storage and release of lithium ion, or a multi-layer structure comprising a third layer (23) containing lithium in addition to the above first layer and the second layer. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a secondary battery, particularly a lithium secondary battery, and a method for producing the secondary battery.

[0002]

2. Description of the Related Art With the widespread use of mobile terminals such as mobile phones and notebook computers, the role of a secondary battery serving as a power source thereof has been emphasized. These secondary batteries are small, lightweight,
Moreover, it is required to have a high capacity and to be resistant to deterioration even after repeated charging and discharging. Metal lithium may be used for the negative electrode of these secondary batteries from the viewpoint of high energy density and light weight, but the metal lithium negative electrode has needle-like crystals on the lithium surface during charging as the charge / discharge cycle progresses. (Dendrite) is deposited, and this crystal penetrates the separator to cause an internal short circuit, which shortens the life of the battery.

Further, it has been considered to use a lithium alloy represented by a composition formula of Li _x M (M is a metal such as Al) as a negative electrode. However, the lithium alloy negative electrode has a lithium ion content per unit volume of lithium ions. Although it has a large amount of occlusion / desorption and a high capacity, it expands and contracts due to the occlusion / release of lithium ions, which causes pulverization along with the progress of charge / discharge cycles, which leads to the problem of short charge / discharge cycle life. there were.
Furthermore, when a carbon material such as graphite or hard carbon capable of inserting and extracting lithium ions is used as the negative electrode,
Charge and discharge cycles are good, but graphite materials have a smaller capacity than metallic lithium and lithium alloys, and hard carbon has a large irreversible capacity in the first charge and discharge, and the energy density is small due to low charge and discharge efficiency. was there.

Therefore, many studies have been conducted for the purpose of improving the negative electrode. Japanese Unexamined Patent Application Publication No. 2000-21392 discloses that metallic lithium is electrically brought into contact with a negative electrode containing a carbon material and a metal such as Si, Ge, Sn, or an oxide thereof when manufacturing a battery, Improvements in over-discharge resistance and cycle characteristics have been proposed. JP-A-11-135120
The publication discloses that a material obtained by coating particles of Al, Sn, Sb or the like with a carbonaceous material is used as a negative electrode, and proposes improvement of high capacity, high voltage and cycle characteristics.

Japanese Patent Laid-Open No. 10-21964 discloses Sn, A
It has been disclosed to use a material mainly composed of a chalcogen compound such as l or Si or an oxide thereof as a negative electrode, and it has been proposed to improve the capacity, cycle characteristics, and production efficiency. Japanese Patent Laid-Open No. 2000-182602 discloses a negative electrode for a secondary battery in which a metal foil mainly composed of lithium is attached to a negative electrode sheet made of an amorphous oxide capable of occluding and releasing lithium. Improvements in capacity and overcharge resistance have been proposed. Japanese Patent Laid-Open No. 2001-15172,
A negative electrode for a secondary battery in which a metal foil mainly containing lithium is attached to a negative electrode sheet made of a carbon material has been disclosed, and high capacity and improvement of charge / discharge efficiency have been proposed.

[0006]

However, the prior art has the following problems. JP-A-2000-21392, JP-A-11-135120, and JP-A-10-21964
According to the technique described in the publication, the metal and the metal oxide have a large irreversible capacity in the first charge and discharge and a large weight of the negative electrode, so that it is difficult to sufficiently increase the energy density of the battery. In addition, when a metal and a carbon-based material are mixed, a voltage flat portion peculiar to the metal is formed in the discharge curve at a voltage higher than that of carbon, so that the operating voltage is lower and higher than that when only carbon is used as the negative electrode. It is difficult to obtain operating voltage. The lower limit voltage of the lithium secondary battery is set according to the application, and the lower the operating voltage, the narrower the usable area becomes. As a result, it is difficult to increase the capacity in the area where the battery is actually used. .

In the method described in JP-A-2000-21392, the added lithium reacts with active functional groups on the carbon surface, water adsorbed on the carbon surface, or water contained in the electrolytic solution solvent or electrolytic solution to form a negative electrode. Since a film is formed on the surface and lithium contained in such a film is electrochemically inactive and cannot contribute to the charge / discharge capacity of the battery, the charge / discharge efficiency is not sufficiently improved. Further, these coatings have a large electric resistance and increase the resistance of the battery, so that the effective capacity of the battery is rather reduced. In the method described in JP-A-2000-182602, and JP-A-2001-15172, the amorphous material, and the carbon material negative electrode sheet, both the electrode binder is in direct contact with the lithium metal foil The binder and a part of the lithium metal foil react to form a high resistance film. Further, in the case of a sheet made of an amorphous material, it is inevitable that the metal distribution is nonuniform on a microscopic scale, and as a result, local concentration of the electric field occurs. For these reasons, it is difficult to maintain high level cycle characteristics.

Regarding the electrolytic solution, the following descriptions are given in the respective publications. That is, JP-A-2000-21392 discloses 65.
0.4 parts by weight of LiBF ₄ and 12.1 parts by weight of L in a mixed solvent consisting of 5 parts by weight of diethyl carbonate and 22 parts by weight of ethylene carbonate.
An electrolytic solution obtained by dissolving iPF ₆ is disclosed in JP-A No. 11-135120, and 1 mol / l of LiPF ₆ is added to a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1.
Dissolved electrolytic solution, JP-A-10-21964,
An electrolytic solution prepared by dissolving 1 mol / l of LiPF ₆ in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 2: 8 is disclosed in Japanese Patent Laid-Open No. 2000-182602 in which 65.3 g of diethyl carbonate and 22.2 g of ethylene carbonate are used. In mixed solvent
An electrolytic solution obtained by dissolving 0.4 g of LiBF ₄ and 12.1 g of LiPF ₆ is disclosed in JP 2001-15172 A, in which 0.4 g of LiBF is mixed with a mixed solvent of 65.3 g of diethyl carbonate and 22.2 g of ethylene carbonate. ₄ and 12.1 g of LiPF ₆
Dissolved in 1,2-bis (ethoxycarbonyl)
An electrolytic solution prepared by dissolving an additive such as -1,2-dimethylhydrazine is described in each Example. In addition, various solvents are listed in the text, and it is described that they can be used as an electrolytic solution. However, no detailed description has been made regarding the solvent composition of the electrolytic solution, the mixing volume ratio, and the optimum value / range of the lithium salt concentration.

In view of the above problems of the prior art, the present invention substantially improves the battery capacity in the voltage range in which the battery is actually used while maintaining high charge / discharge efficiency and good cycle characteristics. It is intended to provide a lithium secondary battery.

[0010]

According to the present invention, (i)
Mainly composed of a positive electrode containing a lithium-containing composite oxide, (ii) a first layer (21) containing carbon as a main component, and a material having lithium ion conductivity and capable of inserting and extracting lithium ions. A negative electrode having a multilayer structure including a second layer (22) as a component, and (iii) a relative dielectric constant of 30 or more, and
A first non-aqueous solvent having a viscosity of 1 cP or more, a relative dielectric constant of 10 or less,
A mixed solvent containing a second non-aqueous solvent having a viscosity of less than 1 cP in a volume ratio of 2: 8 to 6: 4 and a lithium salt dissolved in a range of 0.5 to 1.5 mol / l. A lithium secondary battery comprising a non-aqueous electrolyte,
And (i) a positive electrode containing a lithium-containing composite oxide, (i
i) a first layer containing carbon as a main component, a second layer containing a material having lithium ion conductivity and capable of absorbing and releasing lithium ions as a main component, and lithium. A negative electrode having a multilayer structure including a third layer that does not come into direct contact with the first layer, and (iii) a relative dielectric constant 30
A mixed solvent containing the first non-aqueous solvent having a viscosity of 1 cP or more and the second non-aqueous solvent having a relative dielectric constant of 10 or less and a viscosity of less than 1 cP in a volume ratio of 2: 8 to 6: 4. And a non-aqueous electrolyte solution in which a lithium salt is dissolved in the range of 0.5 to 1.5 mol / l.

The present invention will be described in detail below. As described above, by using a negative electrode in which a carbon material for a negative electrode and a material having a large lithium absorption / desorption amount such as a metal oxide are used, it is possible to achieve both a high lithium absorption / desorption amount and charge / discharge efficiency. Can be inferred theoretically possible.
Furthermore, it is considered that the irreversible capacity of the battery is reduced and the energy density can be improved by adding metallic lithium in an amount corresponding to the irreversible capacity of the negative electrode to the carbon material for the negative electrode. However, it is difficult to actually improve the energy density of the battery simply by combining these materials, and this point is as described in the section of the prior art.

Therefore, in the present invention, as the structure of the negative electrode, the first layer containing carbon as the main component, and (a) lithium ion conductivity, and capable of absorbing and desorbing lithium ions. A multilayer structure including a second layer containing a material as a main component, or (b) the second layer, and
A multi-layered structure including a third layer made of lithium or a lithium-containing compound and arranged so that the first layer and the third layer are not in direct contact with each other is adopted. That is, a layer containing carbon as its main component and a layer containing as its main component a material capable of inserting and extracting lithium ions other than carbon are formed.

In the secondary battery of the present invention having such a structure, by using the film material, the active material is uniformly present on the negative electrode, and the electric field distribution between the positive electrode and the negative electrode becomes uniform. Therefore, local concentration of the electric field is unlikely to occur,
Stable battery characteristics can be obtained without damage such as peeling of the active material from the current collector even after a cycle. When the electric field distribution is not uniform, the lithium storage layer may locally expand in volume, which causes deterioration of battery characteristics. Impurities such as a binder may react with metallic lithium to form a film having high resistance and deteriorate battery characteristics. The negative electrode according to the present invention using a film material can solve such a problem.

In the case of the embodiment including the third layer of (b) above,
The second layer between the first layer and the third layer suppresses the direct reaction between the active sites on the surface of the carbon negative electrode and metallic lithium, and the added lithium is effective for filling the irreversible capacity of the carbon negative electrode. I am trying to work. In addition, a part of the added lithium is doped into a material having lithium ion conductivity, which increases the lithium ion concentration of the film material and increases the number of charge carriers in the film material. Is further improved. Thereby, the resistance of the battery can be reduced and the effective capacity of the battery is further improved.
It is also possible to provide a negative electrode for a lithium secondary battery, which has a region containing lithium in excess of the theoretical composition in a fully charged state.

When the negative electrode in which the second layer is arranged between the first layer and the third layer is charged, a part of lithium constituting the third layer is doped into the second layer. By utilizing this phenomenon, the second layer is doped with lithium in excess of the saturation amount in a fully charged state without consuming the lithium contained in the positive electrode, and the negative electrode in which the second layer is doped with lithium is obtained. be able to. When charge and discharge are repeated for a negative electrode having a multilayer structure including the first to third layers, lithium contained in the third layer is doped in the first layer and the second layer,
The third layer gradually disappears, and in the process, the second layer containing lithium is formed. Such a negative electrode having the second layer containing lithium contributes to the realization of excellent battery performance by itself from the viewpoint different from that of the three-layer structure.

In the lithium secondary battery thus produced, unlike the prior art in which metallic lithium is brought into electrical contact with the negative electrode during battery production, a film with a large electric resistance is not formed, so the effective capacity of the battery is increased. It becomes possible to raise. The structure in which the carbon-containing layer and the lithium-containing layer are laminated,
By utilizing the advantages of both, a high lithium storage amount can be realized without causing dendrites.

However, as described in the section of the prior art, in the structure in which the lithium layer is in direct contact with the carbon layer, lithium and carbon react at the interface to form a highly insulating film, which results in battery characteristics. Is a problem. This problem is mitigated by applying a lithium alloy layer instead of the lithium layer, but in this case also, there is a problem in that the battery performance is deteriorated due to the reaction of lithium in the lithium alloy with the carbon layer. On the other hand, the second layer of the present invention related to the lithium secondary battery including the third layer originally has lithium ion conductivity, and lithium is doped by charge / discharge to further improve lithium ion conductivity. improves. Such a film having high lithium ion conductivity does not hinder the charge / discharge reaction, but rather suppresses a side reaction between the electrolytic solution and the active material as a protective film and improves battery characteristics. That is, by providing the second layer, and further the third layer in a film shape on the first layer containing carbon as a main component,
Intercalation between carbon layers in the state where lithium ions are solvated is suppressed, deterioration of the carbon layer is prevented, and cycle characteristics are improved.

On the other hand, however, by providing the second layer and the third layer in the form of a film on the first layer containing carbon as a main component, the relative dielectric constant is 30 or more and the viscosity is 1 cP or more. When using only the non-aqueous solvent of the electrolytic solution solvent, the viscosity of the electrolytic solution is high, it is difficult to penetrate the first layer of the electrolytic solution,
The interfacial resistance of the electrodes rises, and the battery performance cannot be fully obtained. Further, when only a non-aqueous solvent having a relative dielectric constant of 10 or less and a viscosity of less than 1 cP is used as the electrolyte solvent,
Although the solvent easily reaches the first layer, the dissociation of the lithium salt is insufficient due to the low relative dielectric constant, and the ionic conductivity of the electrolyte is insufficient, increasing the internal resistance of the battery and Will not be able to bring out the full performance of. As a result of investigations by the present inventors, in the above-described laminated structure, the relative dielectric constant of 30
The first non-aqueous solvent and the second non-aqueous solvent having a viscosity of 1 cP or more and a second non-aqueous solvent having a relative dielectric constant of 10 or less and a viscosity of less than 1 cP are used respectively. The mixing volume ratio of the non-aqueous solvent is within the range of 2: 8 to 6: 4, and the lithium salt is added in an amount of 0.5 mol / l to 1.5 mo.
It has been found that the use of a non-aqueous electrolytic solution that is dissolved within the range of 1 / l makes it possible to achieve both penetration of the electrolytic solution and dissociation of the lithium salt. Therefore, in the present invention, the non-aqueous electrolytic solution having such a structure is used.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The shape of the secondary battery of the present invention is not particularly limited, and examples thereof include a cylindrical type, a square type, and a coin type. In the present invention, the first, second, and third layers are carbon, a film-like lithium storage material, and lithium,
Alternatively, a compound containing lithium is contained as a main component, but an additive or the like may be contained as appropriate. Further, in the present invention, the main component means a case where the content is more than 50% by weight and up to 100%. Each layer may be singular or plural, but in principle, does not include the configurations shown below.

(I) A structure in which the first layer and the third layer are in direct contact with each other. (Ii) A configuration in which the first layer is arranged on the outermost surface of the negative electrode.

The stacking order is arbitrary except the above-mentioned structure. For example, a structure in which the second layer and the third layer are sequentially stacked on the upper part and the lower part of the first layer is possible. In addition, the battery capacity can be further improved while maintaining good cycle characteristics.

In the present invention, the second layer is mainly composed of a film material having lithium ion conductivity. Here, the lithium ion conductivity means a property in which a current flows through a substance using lithium ions as a carrier of electric charges. The film-like material means a material forming a film with a substantially uniform composition, unlike a particle-like material, and means a film formed by a method such as a vapor deposition method, a CVD method or a sputtering method. For example, a particulate material having lithium ion conductivity which is solidified with a binder is not included in the film material of the present invention.

The second layer is preferably made of a material capable of inserting and extracting lithium ions, in addition to the above-mentioned lithium conductivity. A material capable of absorbing and releasing lithium ions refers to a material capable of incorporating lithium into the material. As a form of incorporating lithium, in addition to a form of forming an alloy or the like, an alloy with the material is formed. It also includes a form in which lithium is incorporated into the structure without doing so. Furthermore, the second layer preferably has an amorphous structure. Electrochemical lithium doping and dedoping of amorphous structure
Since it occurs at a potential lower than the crystal structure, a high operating voltage,
In addition, the battery capacity can be increased while maintaining high charge / discharge efficiency. Here, amorphous is CuKα
The X-ray diffraction method using X-rays has a broad scattering band having vertices at 15 to 40 degrees in the 2θ value. Since the amorphous structure is crystallographically isotropic as compared with the crystal structure, the amorphous structure has excellent strength against external stress and is chemically stable. That is, since it is unlikely to be affected by the expansion and contraction of the negative electrode due to charge and discharge and does not easily react with the electrolytic solution, the stability is excellent when the charge and discharge cycle is repeated, and the capacity deterioration is less likely to occur.

The second layer is preferably a layer formed by a vapor deposition method, a CVD method or a sputtering method. When these film forming methods are used, an amorphous ion conductive film is uniformly obtained on the negative electrode. This film makes the electrolytic distribution between the positive electrode and the negative electrode uniform. Therefore, local concentration of the electric field does not occur, damage such as peeling of the active material from the current collector does not occur even after a cycle, and stable battery characteristics can be obtained. The material forming the second layer in the present invention is not particularly limited as long as it has lithium ion conductivity and is capable of inserting and extracting lithium ions, but Si, Ge, In, It is preferable to contain one or more elements selected from the group consisting of Sn, Pb, and oxides thereof. By selecting the material and having an amorphous structure,
The battery capacity can be increased while maintaining a high operating voltage and a high charging / discharging efficiency, which facilitates manufacturing. In particular, Si, Sn, and oxides thereof have a small structural change when lithium is occluded, and are less likely to deteriorate even after repeated charging and discharging, and thus good cycle characteristics can be obtained.

In the present invention, the substance constituting the third layer is not particularly limited as long as it is lithium or a compound containing lithium, but preferably metallic lithium, lithium alloy, lithium nitride, Li _3-x M _x. N (M = Co, Ni,
Cu) and mixtures thereof. Since such a material can electrochemically release a large amount of lithium, it can supplement the irreversible capacity of the negative electrode and improve the charge / discharge efficiency of the battery. The substance forming the third layer preferably has an amorphous structure. The amorphous structure is
Compared with the crystal structure, it is crystallographically isotropic, so it has excellent strength against external stress, and it is chemically stable and does not easily cause side reactions with the electrolytic solution. Lithium contained is efficiently used to supplement the irreversible capacity of the negative electrode. The material forming the third layer is a vapor deposition method, CV
It is preferably a layer formed by the D method or the sputtering method. When these film forming methods are used, a uniform amorphous layer can be formed over the entire negative electrode. Further, since it is not necessary to use a solvent, a side reaction is unlikely to occur, and a layer of higher purity can be produced, and lithium contained in the third layer is efficiently used for filling the irreversible capacity of the negative electrode.

FIG. 1 is a vertical cross-sectional view illustrating a negative electrode of a lithium secondary battery having a multilayer structure according to a first embodiment of the present invention, and FIG. 2 is a multilayer structure according to a second embodiment of the present invention. FIG. 3 is a vertical cross-sectional view illustrating a negative electrode of a lithium secondary battery having a. FIG. 1 shows a first layer (21) containing carbon as a main component on a negative electrode current collector (20) and a material having lithium ion conductivity and capable of inserting and extracting lithium ions. 3 illustrates a negative electrode having a multilayer structure in which a second layer (22) containing as a main component is sequentially stacked. FIG. 2 shows a first layer (21) containing carbon as a main component on a negative electrode current collector (20) and a material having lithium ion conductivity and capable of inserting and extracting lithium ions. And a third layer (23) made of lithium or a lithium-containing compound in that order, and a first layer (21) and a third layer (23). ) Illustrates a negative electrode having a multi-layer structure arranged so as not to come into direct contact with.

The current collector (20) is an electrode for taking out an electric current to the outside of the battery or taking an electric current into the battery from the outside during charging and discharging. The current collector (20) may be any conductive metal foil, and for example, aluminum, copper, stainless steel, gold, tungsten, molybdenum, or the like can be used. The first layer (21), which is a carbon negative electrode layer, is a negative electrode member that occludes or releases lithium during charge and discharge. The carbon negative electrode (21) is made of carbon capable of occluding lithium, and graphite, hard carbon, amorphous carbon, fullerene, carbon nanotube, DLC, or a mixture thereof can be used.

The negative electrode second layer (22) is made of a material having lithium ion conductivity and capable of inserting and extracting lithium ions. As such a material,
In addition to Si, Ge, In, Sn, Pb, and their oxides described above, boron oxide, phosphorus oxide, aluminum oxide, and their composite oxides are listed. These may be used alone or in combination of one or more. It can be used in combination. Further, lithium halide, lithium chalcogenide, or the like may be added to these to increase the lithium ion conductivity. Further, this material is preferably amorphous as described above. By using an amorphous material, the potential at which lithium is doped or dedoped can be made lower than that of crystals, and as a result, the operating voltage of the battery can be increased. The negative electrode second layer (22) is
As described above, it is preferably formed by the CVD method, the vapor deposition method, or the sputtering method. By using these methods, the amorphous layer can be formed with uniform film quality and film thickness. In addition, the negative electrode second layer (2
It is also possible to dope B), P, As, and Sb into 2) to lower the resistivity.

The third layer (23) of the negative electrode is made of lithium or a compound containing lithium. Such materials include metallic lithium, lithium alloys, lithium nitride, Li
_{3-x M x N (M} = Co, Ni, Cu), and mixtures thereof, can be used in combination singly or one or more. Also, this material is preferably amorphous. By using an amorphous material, side reactions with the electrolytic solution can be suppressed, and lithium contained in the material can be efficiently used for filling the irreversible capacity. As a result, the initial charge / discharge efficiency of the battery is improved and the energy density can be increased. The negative electrode third layer (23) is preferably formed by a CVD method, a vapor deposition method, or a sputtering method. By using these methods, the amorphous layer can be formed with uniform film quality and film thickness.

FIG. 3 is a vertical cross-sectional view illustrating a negative electrode of a lithium secondary battery having a multi-layer structure according to the third embodiment of the present invention, and FIG. 4 is a multi-layer structure according to the fourth embodiment of the present invention. FIG. 3 is a vertical cross-sectional view illustrating a negative electrode of a lithium secondary battery having a. The embodiment of FIG. 3 is similar to the first embodiment shown in FIG. 1, and has a structure in which a carbon negative electrode first layer (21) and a negative electrode second layer (22) are sequentially laminated on both surfaces of a current collector (20). Is. The embodiment of FIG. 4 is similar to the second embodiment shown in FIG. 2, and has a carbon negative electrode first layer (21), a negative electrode second layer (22) and a negative electrode third layer on both sides of the current collector (20). It has a structure in which layers (23) are sequentially laminated.

FIG. 5 is a vertical cross-sectional view illustrating a negative electrode of a lithium secondary battery having a multilayer structure according to a fifth embodiment of the present invention. In this embodiment, the carbon negative electrode first layer (21) is formed on the current collector (20), and the saturated lithium layer (24) is formed thereon. In the saturated lithium layer (24), a region containing lithium in excess of the saturation amount in a fully charged state, that is, a region containing lithium in excess of the theoretical composition is formed. The saturation amount (theoretical composition) of lithium means that when a substance and lithium form a compound,
The maximum value of lithium that can be contained in the compound. The saturated lithium layer (24) corresponds to the negative electrode second layer (22) of the first to fourth embodiments and is included in the present invention. The amount of lithium saturation in various lithium alloys can be found, for example, in “Electronic Materials” (April 2001, Vol. 40, No. 4, p. 78, issued April 1, 2001, published by the Industrial Research Board). There is a description. The values shown below are the upper limits of the lithium alloy composition, and alloys containing lithium in excess of this composition ratio cannot be obtained by ordinary alloy production methods.

LiSi alloy: Li ₄ Si LiAl alloy: LiAl LiSn alloy: Li _4.4 Sn LiCd alloy: Li ₃ Cd LiSb alloy: Li ₃ Sb LiPb alloy: Li _4.4 Pb LiZn alloy: LiZn LiBi alloy: Li ₃ Bi

The negative electrode of FIG. 5 has a saturated lithium layer (2) containing a lithium compound containing such a saturated amount of lithium.
4) have. Such a lithium compound is obtained, for example, by charging and discharging the negative electrode having the structure shown in FIG. 2 under predetermined conditions. Although FIG. 5 shows an example in which a uniform saturated lithium layer (24) is formed on the carbon negative electrode first layer (21), a layer made of lithium is formed on the surface of the saturated lithium layer (24). The formed structure and the like are also included in the present invention.
In the present invention, as described above, the electrolytic solution contains 0.5 mol / mol of lithium salt in the mixed solvent in which the mixing volume ratio of the first non-aqueous solvent and the second non-aqueous solvent is within the range of 2: 8 to 6: 4. The non-aqueous electrolytic solution is prepared by dissolving it within the range of 1 to 1.5 mol / l. If the ratio of the first non-aqueous solvent is less than 2, the relative permittivity of the mixed solvent is low, the dissociation of the lithium salt becomes insufficient,
Since the ionic conductivity of the electrolytic solution is insufficient, the internal resistance of the battery rises, and the battery performance cannot be fully obtained. When the ratio of the first non-aqueous solvent exceeds 6, the viscosity of the electrolytic solution becomes high, it is difficult for the electrolytic solution to permeate into the first layer, the electrode interface resistance increases, and the battery performance is sufficiently improved. I can't withdraw. On the other hand, if the concentration of the lithium salt is outside the above range, the electric conductivity of the electrolytic solution will be insufficient, and the internal resistance of the battery will increase, so that the battery performance cannot be fully obtained. The particularly preferable range of the mixing volume ratio of the first non-aqueous solvent and the second non-aqueous solvent is 3: 7 to 5: 5, and the particularly preferable range of the lithium salt concentration is 0.8 mol / l to 1.2 mol / l. is there.

Examples of the first non-aqueous solvent of the present invention include ethylene carbonate, propylene carbonate and butylene carbonate, and the second non-aqueous solvent includes
Examples include 1,2-dimethoxyethane, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. In the present invention, the lithium salt is L
iBF ₄ , LiPF ₆ , LiCl, LiBr, LiI, L
Examples include iN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ .

In the present invention, the positive electrode is Li _x MO ₂ (M
Is at least one transition metal) lithium-containing composite oxide, such as Li _x CoO ₂ , Li _x NiO ₂ , Li
_x Mn ₂ O ₄ , Li _x MnO ₃ , Li _x Ni _y C _1-y O _2, etc.
A conductive material such as carbon black, a binder such as polyvinylidene fluoride, and the like, which are dispersed and kneaded with a solvent such as N-methyl-2-pyrrolidone, and coated on a substrate such as an aluminum foil can be used. In the present invention, the separator may be a polyolefin such as polypropylene or polyethylene, or a porous film such as a fluororesin.

FIG. 6 is a sectional view illustrating the structure of the secondary battery of the present invention. In the figure, the positive electrode is formed by forming a layer (12) containing a positive electrode active material on a positive electrode current collector (11), and a negative electrode is a layer (13) containing a negative electrode active material. (14)
It is formed by forming a film on top. The positive electrode and the negative electrode are arranged so as to face each other with the electrolytic solution (30) of the aqueous electrolyte solution and the porous separator (50) in the electrolytic solution (30) interposed therebetween. The porous separator (50) is arranged substantially parallel to the layer (13) containing the negative electrode active material.

EXAMPLES The present invention will be described in more detail with reference to the following specific examples. However, as long as the gist of the invention is not exceeded,
The invention is not limited to the examples.

[Example of Positive Electrode Sheet] Li _1.1 Mn ₂ O ₄ , a conductivity-imparting agent, and polyvinylidene fluoride were added to N-methyl-2-
The slurry obtained by dispersing and kneading using pyrrolidone,
A 20 μm-thick aluminum foil that functions as a positive electrode current collector (11) was coated and dried to prepare a positive electrode sheet. The positive electrode sheet was dried and then compressed using a pressing machine.

[Example of Preparation of First Layer of Negative Electrode] A slurry obtained by dispersing and kneading graphite powder, a conductivity-imparting agent, and polyvinylidene fluoride with N-methyl-2-pyrrolidone was used as a negative electrode current collector (20). Applied on a copper foil with a thickness of 10 μm that functions as
It dried and produced the negative electrode 1st layer. The negative electrode first layer was dried and then compressed using a pressing machine.

[Negative Electrode Second Layer Preparation Example-1] A negative electrode second layer was formed on the negative electrode first layer prepared in the negative electrode first layer preparation example by a vacuum evaporation method. , Negative electrode current collector,
A negative electrode sheet having a structure in which a negative electrode first layer and a negative electrode second layer were laminated in this order was produced.

[Negative Electrode Second Layer Preparation Example-2] A negative electrode second layer is formed on the negative electrode first layer prepared in the negative electrode first layer preparation example by a sputtering method, A negative electrode sheet having a structure in which a negative electrode current collector, a negative electrode first layer, and a negative electrode second layer were laminated in this order was produced.

[Negative electrode second layer preparation example-3] A boron oxide layer is formed as a negative electrode second layer on the negative electrode first layer prepared in the negative electrode first layer preparation example by using a vacuum deposition method. Then, a negative electrode sheet having a structure in which the negative electrode current collector, the negative electrode first layer, and the negative electrode second layer were laminated in this order was produced.

[Negative Electrode Third Layer Preparation Example-1] On the negative electrode second layer of the negative electrode sheet prepared in the negative electrode second layer Preparation Example-1, a metallic lithium layer was vacuum-deposited as a negative electrode third layer. A negative electrode sheet having a structure in which a negative electrode current collector, a negative electrode first layer, a negative electrode second layer, and a negative electrode third layer were laminated in this order was manufactured.

[Negative Electrode Third Layer Preparation Example-2] On the negative electrode second layer of the negative electrode sheet prepared in Negative Electrode Second Layer Preparation Example-2, a metallic lithium layer was vacuum-deposited as a negative electrode third layer. A negative electrode sheet having a structure in which a negative electrode current collector, a negative electrode first layer, a negative electrode second layer, and a negative electrode third layer were laminated in this order was manufactured.

[Negative Electrode Third Layer Preparation Example-3] A negative electrode third layer was formed on the negative electrode second layer of the negative electrode second layer Preparation Example-3 by vacuum deposition of a metallic lithium layer as a negative electrode third layer. A negative electrode sheet having a structure in which a negative electrode current collector, a negative electrode first layer, a negative electrode second layer, and a negative electrode third layer were laminated in this order was manufactured.

[Negative Electrode Comparative Example Sheet Preparation Example-1] Graphite powder, Si powder, conductivity-imparting agent, and polyvinylidene fluoride were added N-
The slurry obtained by dispersing and kneading with methyl-2-pyrrolidone has a thickness of 10 μm which functions as a negative electrode current collector (20).
The first layer (2) formed by coating and drying on a copper foil of m, and Si powder (26) dispersed on the negative electrode current collector (20) shown in FIG.
A negative electrode comparative sheet coated with 1) was prepared. The negative electrode comparative example sheet was dried and then compressed using a pressing machine.

[Negative Electrode Comparative Example Sheet Preparation Example-2] A negative electrode current collector and a negative electrode were prepared by forming a metallic lithium layer on the negative electrode first layer prepared in the negative electrode first layer preparation example using a vacuum deposition method. A negative electrode comparative example sheet having a structure in which the first layer and the metallic lithium layer were laminated in this order was produced.

Example 1 Negative Electrode Second Layer Preparation Example 1 A negative electrode sheet prepared in Example 1, a separator made of polypropylene nonwoven fabric, and the positive electrode sheet prepared in the positive electrode sheet preparation example were laminated, and FIG. A battery having the exemplified constitution was produced.
The electrolytic solution was prepared by adding LiPF ₆ to 1.0 in a mixed solvent of ethylene carbonate and diethyl carbonate (mixing volume ratio = 3: 7).
What was dissolved in mol / l was used.

[Example 2] Example of preparation of second layer of negative electrode on negative electrode-
A battery was prepared in the same manner as in Example 1 except that the negative electrode sheet prepared in 2 was used.

[Example 3] Example of preparation of second layer of negative electrode on negative electrode-
A battery was prepared in the same manner as in Example 1 except that the negative electrode sheet prepared in 3 was used.

[Example 4] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was produced in the same manner as in Example 1 except that LiPF ₆ was dissolved in 1.0 mol / l in 2: 8).

[Embodiment 5] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 1 except that LiPF ₆ was dissolved in 6: 4) in an amount of 1.0 mol / l.

Example 6 A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 1, except that 0.5 mol / l of LiPF ₆ was dissolved in 3: 7).

Example 7 A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was produced in the same manner as in Example 1 except that 1.5 mol / l of LiPF ₆ was dissolved in 3: 7).

[Embodiment 8] A mixed solvent of ethylene carbonate and dimethyl carbonate (mixed volume ratio =
A battery was produced in the same manner as in Example 1 except that LiPF ₆ was dissolved in 1.0 mol / l in 3: 7).

[Embodiment 9] LiPF ₆ was added to the electrolytic solution as a mixed solvent of ethylene carbonate, diethyl carbonate and methyl ethyl carbonate (mixing volume ratio = 3: 5: 2).
A battery was prepared in the same manner as in Example 1 except that the solution of 1.0 mol / l was used.

[Embodiment 10] LiPF ₆ was added to an electrolytic solution in a mixed solvent of ethylene carbonate, diethyl carbonate and methyl ethyl carbonate (mixing volume ratio = 3: 2: 5).
A battery was prepared in the same manner as in Example 1 except that the solution of 1.0 mol / l was used.

[Embodiment 11] A mixed solvent of ethylene carbonate, propylene carbonate and diethyl carbonate (mixing volume ratio = 30: 5: 65) was used as an electrolytic solution and LiPF _{6 was used.}
A battery was prepared in the same manner as in Example 1 except that a solution of 1.0 mol / l was used.

[Embodiment 12] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 1 except that LiN (C ₂ F ₅ SO ₂ ) ₂ was dissolved in 1.0 mol / l in 3: 7).

[Example 13] Example of preparation of third layer of negative electrode on negative electrode-
A battery was produced in the same manner as in Example 1 except that the negative electrode sheet produced in 1 was used.

[Example 14] Example of preparation of third layer of negative electrode on negative electrode-
A battery was produced in the same manner as in Example 13 except that the negative electrode sheet produced in 2 was used.

[Example 15] Example of preparation of third layer of negative electrode on negative electrode-
A battery was produced in the same manner as in Example 13 except that the negative electrode sheet produced in 3 was used.

[Example 16] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 13 except that LiPF ₆ dissolved in 1.0 mol / l in 2: 8) was used.

Example 17 A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 13 except that LiPF ₆ was dissolved in 1.0 mol / l in 6: 4).

Example 18 A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was produced in the same manner as in Example 13 except that 0.5 mol / l of LiPF ₆ dissolved in 3: 7) was used.

Example 19 A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 13 except that 1.5 mol / l of LiPF ₆ was dissolved in 3: 7).

Example 20 A mixed solvent of ethylene carbonate and dimethyl carbonate (mixed volume ratio =
A battery was produced in the same manner as in Example 13 except that LiPF ₆ was dissolved in 1.0 mol / l in 3: 7).

[Example 21] LiPF ₆ was added to an electrolytic solution in a mixed solvent of ethylene carbonate, diethyl carbonate and methyl ethyl carbonate (mixing volume ratio = 3: 5: 2).
Example 1 except that a solution of 1.0 mol / l was used.
A battery similar to that of 3 was manufactured.

[Embodiment 22] LiPF ₆ was added to a mixed solvent of ethylene carbonate, diethyl carbonate and methyl ethyl carbonate (mixing volume ratio = 3: 2: 5) as an electrolytic solution.
Example 1 except that a solution of 1.0 mol / l was used.
A battery similar to that of 3 was manufactured.

[Example 23] LiPF ₆ was added to an electrolytic solution in a mixed solvent of ethylene carbonate, propylene carbonate and diethyl carbonate (mixing volume ratio = 30: 5: 65).
A battery was prepared in the same manner as in Example 13 except that the solution of 1.0 mol / l was used.

Example 24 A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 13 except that LiN (C ₂ F ₅ SO ₂ ) ₂ dissolved in 1.03 mol / l was used in 3: 7).

[Comparative Example 1] A battery was manufactured in the same manner as in Example 1 except that the negative electrode sheet prepared in the first negative electrode layer preparation example was used as the negative electrode.

[Comparative Example 2] A battery was prepared in the same manner as in Example 1 except that the negative electrode sheet prepared in the negative electrode comparative example sheet preparation example-1 was used as the negative electrode.

[Comparative Example 3] A battery was prepared in the same manner as in Example 1 except that the negative electrode sheet prepared in the negative electrode comparative example sheet preparation example-2 was used as the negative electrode.

[Comparative Example 4] A mixed solvent of ethylene carbonate and propylene carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 1 except that LiPF ₆ was dissolved in 1.0 mol / l in 1: 1).

[Comparative Example 5] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 1 except that LiPF ₆ was dissolved in 1.0 mol / l in 1: 9).

[Comparative Example 6] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery similar to that of Example 1 was prepared, except that LiPF ₆ was dissolved in 1.0 mol / l in 7: 3).

[Comparative Example 7] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was produced in the same manner as in Example 1 except that 0.4 mol / l of LiPF ₆ was dissolved in 3: 7).

[Comparative Example 8] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 1 except that 1.6 mol / l of LiPF ₆ was dissolved in 3: 7).

[Comparative Example 9] A mixed solvent of ethylene carbonate and propylene carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 13 except that 1: 1) LiPF ₆ dissolved in 1.0 mol / l was used.

[Comparative Example 10] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 13, except that 1.0 mol / l of LiPF ₆ was dissolved in 1: 9).

[Comparative Example 11] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 13 except that LiPF ₆ was dissolved in 1.0 mol / l in 7: 3).

[Comparative Example 12] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was prepared in the same manner as in Example 13 except that 0.4 mol / l of LiPF ₆ was dissolved in 3: 7).

[Comparative Example 13] A mixed solvent of ethylene carbonate and diethyl carbonate (mixed volume ratio =
A battery was produced in the same manner as in Example 13, except that 1.6 mol / l of LiPF ₆ was dissolved in 3: 7).

A charge / discharge cycle test was conducted on the batteries of Examples 1 to 24 and Comparative Examples 1 to 13 at a test voltage of 3.0 to 4.3V. The results of the first charge and discharge and the capacity retention ratio with respect to the first discharge capacity after the lapse of 300 cycles are shown in Table 1 for Examples and Table 2 for Comparative Examples.

[0086]

[Table 1]

[0087]

[Table 2]

While the charge and discharge efficiency of Comparative Example 1 using only the carbon material for the negative electrode was 93.2%, Examples 1 to 3 in which the second layer of the negative electrode made of Si or boron oxide was formed.
The charging / discharging efficiency of was about 93%, which was comparable to the carbon material alone. Furthermore, in Examples 13 to 15 in which a negative electrode third layer made of metallic lithium was formed, from 98.2
As high as 98.9%, it was revealed that the irreversible capacity of the negative electrode was compensated efficiently by the third layer of the negative electrode. On the other hand, Comparative Example 2 in which Si powder is dispersed in a carbon material, and Comparative Example 3 in which a metallic lithium layer is directly formed on the surface of the carbon material.
Then, the charge and discharge efficiencies are 60.2% and 72.6%,
It has been clarified that the charge / discharge efficiency cannot be improved in the configuration in which the crystalline material is dispersed in the carbon material and the configuration in which the lithium layer is formed on the carbon material. Further, the capacity retention rate after 300 cycles is about 88.6 to 90.3% with respect to the initial discharge capacity in Examples 1 to 3 and 13 to 15, while in Comparative Examples 2 and 3, 32.6 each
% And 18.5%, it was revealed that the cycle characteristics could not be improved with the structure of the comparative example.

In Comparative Example 2, the electrical contact of the negative electrode layer was lost due to the expansion and contraction of the Si powder during charging and discharging, and the resistance increased. In Comparative Example 3, the lithium formed on the carbon material changed to carbon. It is considered that this is due to the formation of a high-resistance film by reacting with the active sites on the surface. From the results of Examples 1 to 3 and 13 to 15, it was shown that the secondary battery having the negative electrode configuration of the present invention has high capacity and charge / discharge efficiency, and has stable cycle characteristics.

In Examples 1 to 24 in which the composition of the electrolytic solution solvent, the mixing volume ratio, and the lithium salt concentration were within the scope of the present invention, the initial charge / discharge efficiency was as high as about 92 to 99%, and 300
The capacity retention rate after cycling was also maintained at about 85 to 90%, while in Comparative Examples 4 to 13 carried out with a solvent composition, a mixing volume ratio, and a lithium salt concentration outside the scope of the present invention, lithium was used. When the salt concentration is 1.6 mol / l (Comparative Examples 8 and 13), the charge / discharge efficiency is about 80%, but in the other Comparative Examples, the efficiency is poor at about 25 to 48%. Further, the cycle characteristics were 30 except for Comparative Examples 8 and 13.
The capacity could not be retained up to 0 cycles, and Comparative Examples 8 and 13
The capacity retention rate is low at around 40%. It is considered that when the solvent composition, the mixing volume ratio, and the lithium salt concentration are out of the range of the present invention, the electrode interfacial resistance or the internal resistance of the battery increases, and the battery performance cannot be sufficiently brought out. From the results of Examples 1 to 24, it was shown that the electrolytic solution composition, the mixing volume ratio, and the lithium salt concentration of the present invention are within the effective range for the negative electrode constitution of the present invention.

[0091]

As described above, according to the present invention, as the constitution of the negative electrode, the first layer containing carbon as the main component, and having lithium ion conductivity, and absorbing and releasing lithium ions. A multilayer structure containing a second layer containing a material that can be a main component, or the second layer, further containing a third layer of lithium or a lithium-containing compound, and the first By adopting a multilayer structure in which the layer and the third layer are arranged so as not to come into direct contact, and by optimizing the solvent composition of the electrolytic solution, the mixing volume ratio, and the lithium salt concentration in the negative electrode configuration, Both charge and discharge efficiency and capacity can be achieved at the same time, and good cycle characteristics can be realized.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view illustrating a negative electrode of a lithium secondary battery according to a first embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view illustrating a negative electrode of a lithium secondary battery according to a second embodiment of the present invention.

FIG. 3 is a vertical cross-sectional view illustrating a negative electrode of a lithium secondary battery according to a third embodiment of the present invention.

FIG. 4 is a vertical cross-sectional view illustrating a negative electrode of a lithium secondary battery according to a fourth embodiment of the present invention.

FIG. 5 is a vertical cross-sectional view illustrating a negative electrode of a lithium secondary battery according to a fifth embodiment of the present invention.

FIG. 6 is a cross-sectional view illustrating the structure of a secondary battery of the present invention.

FIG. 7 is a diagram showing an example of a cross-sectional structure of a negative electrode of a comparative example.

[Explanation of symbols]

20 Negative electrode current collector 21 First layer (carbon negative electrode layer) 22 Second layer 23 Third Layer 24 Saturated lithium layer

Front page continuation (51) Int.Cl. ⁷ identification code FI theme code (reference) H01M 4/56 H01M 4/56 4/58 4/58 (72) Inventor Mariko Miyaji 5-7 Shiba, Minato-ku, Tokyo No. 1 Inside the NEC Corporation (72) Inventor Ikiko Yamazaki 5-7 Shiba, Minato-ku, Tokyo No. 1 Inside the NEC Corporation (72) Kouji Utsuki 5-7-1 Shiba, Minato-ku, Tokyo No. Nippon Electric Co., Ltd. (72) Inventor Jiro Iriyama 5-7-1, Shiba, Minato-ku, Tokyo Nippon Electric Co., Ltd. (72) Inventor Tamaki Miura 5-7-1, Shiba, Minato-ku, Tokyo Japan Electric company (72) Inventor Morihiro Mori 5-7-1, Shiba, Minato-ku, Tokyo Nippon Electric Co., Ltd. In-house (72) Hidemasa Kawai 5-7-1, Shiba, Minato-ku, Tokyo NEC Corporation In-company F-term (reference) 5H029 AJ03 AJ05 AK03 AL01 AL02 AL06 AL07 AL08 AL11 AL12 AM03 AM04 AM05 AM07 CJ24 DJ18 EJ12 HJ07 HJ10 HJ20 5H050 AA07 AA08 BA16 BA17 CA08 CA09 CB01 CB02 CB07 CB0 8 CB11 CB12 DA13 DA18 EA24 FA20 GA24 HA07 HA10 HA19

Claims (9)

[Claims] 1. A positive electrode containing (i) a lithium-containing composite oxide, (ii) a first layer (21) containing carbon as a main component, having lithium ion conductivity and occluding lithium ions, and Second layer based on materials that can be released (22)
And (iii) a first non-aqueous solvent having a relative permittivity of 30 or more and a viscosity of 1 cP or more, and a second non-aqueous solvent having a relative permittivity of 10 or less and a viscosity of less than 1 cP. A mixed solvent containing a solvent in a volume ratio of 2: 8 to 6: 4, comprising a non-aqueous electrolyte solution in which a lithium salt is dissolved in a range of 0.5 to 1.5 mol / l. Characteristic lithium secondary battery. 2. A positive electrode containing (i) a lithium-containing composite oxide, (ii) a first layer (21) containing carbon as a main component, having lithium ion conductivity and occluding lithium ions, and A second layer (2) based on a material that can be released
2) and a negative electrode having a multi-layer structure containing lithium and a third layer (23) which does not come into direct contact with the first layer (21), and (iii) a relative dielectric constant of 30 or more and a viscosity. A mixed solvent containing a first non-aqueous solvent of 1 cP or more and a second non-aqueous solvent having a relative dielectric constant of 10 or less and a viscosity of less than 1 cP in a volume ratio of 2: 8 to 6: 4, which is a lithium salt. And a non-aqueous electrolyte solution dissolved in the range of 0.5 to 1.5 mol / l. 3. The second layer (22) comprises Si, Ge, Sn, I
The lithium secondary battery according to claim 1 or 2, containing one or more components selected from the group consisting of n, Pb, and oxides thereof. 4. The second layer (22) comprises a vapor deposition method, a CVD method,
Alternatively, the lithium secondary battery according to any one of claims 1 to 3, which has an amorphous structure formed by a sputtering method. 5. The method according to claim 2, wherein the third layer (23) comprises one or more materials selected from the group consisting of metallic lithium, lithium alloys, and lithium nitride. Lithium secondary battery. 6. The third layer (23) comprises a vapor deposition method, a CVD method,
Alternatively, the lithium secondary battery according to any one of claims 2 to 5, which has an amorphous structure formed by a sputtering method. 7. The first non-aqueous solvent is one or more non-aqueous solvents selected from the group consisting of ethylene carbonate, propylene carbonate, and butylene carbonate, and the second non-aqueous solvent is 1, The lithium secondary battery according to any one of claims 1 to 6, which is one or more non-aqueous solvent selected from the group consisting of 2-dimethoxyethane, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate. 8. The lithium salt is LiBF ₄ , LiPF ₆ ,
LiCl, LiBr, LiI, LiN (CF ₃ S
The lithium secondary battery according to claim 1, which is one or more lithium salts selected from the group consisting of O ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ . 9. A positive electrode containing (i) a lithium-containing composite oxide, (ii) a first layer (21) containing carbon as a main component, having lithium ion conductivity and occluding lithium ions,
And a second layer (22) containing a material capable of being released as a main component, and the first layer (21) containing lithium and
Charging and / or discharging the negative electrode of a lithium secondary battery comprising a negative electrode having a multilayer structure including a third layer (23) not in direct contact with (iii) a non-aqueous electrolyte, and A method for producing a lithium secondary battery, which comprises doping the second layer with lithium contained in the layer to produce a second layer containing lithium.